Thermal inkjet print cartridges operate by rapidly heating a small volume of ink to cause the ink to vaporize and be ejected through one of a plurality of orifices so as to print a dot of ink on a recording medium, such as a sheet of paper. Typically, the orifices are arranged in one or more linear arrays in a nozzle member. The properly sequenced ejection of ink from each orifice causes characters or other images to be printed upon the paper as the printhead is moved relative to the paper. The paper is typically shifted each time the printhead has moved across the paper. The thermal inkjet printer is fast and quiet, as only the ink strikes the paper. These printers produce high quality printing and can be made both compact and affordable.
In one prior art design, the inkjet printhead generally includes: (1) ink channels to supply ink from an ink reservoir to each vaporization chamber proximate to an orifice; (2) a metal orifice plate or nozzle member in which the orifices are formed in the required pattern; and (3) a silicon substrate containing a series of thin film resistors, one resistor per vaporization chamber.
To print a single dot of ink, an electrical current from an external power supply is passed through a selected thin film resistor. The resistor is then heated, in turn superheating a thin layer of the adjacent ink within a vaporization chamber, causing explosive vaporization, and, consequently, causing a droplet of ink to be ejected through an associated orifice onto the paper.
One prior art print cartridge is disclosed in U.S. Pat. No. 4,500,895 to Buck et al., entitled "Disposable Inkjet Head," issued Feb. 19, 1985 and assigned to the present assignee.
In one type of prior art inkjet printhead, described in U.S. Pat. No. 4,683,481 to Johnson, entitled "Thermal Ink Jet Common-Slotted Ink Feed Printhead," ink is fed from an ink reservoir to the various vaporization chambers through an elongated hole formed in the substrate. The ink then flows to a manifold area, formed in a barrier layer between the substrate and a nozzle member, then into a plurality of ink channels, and finally into the various vaporization chambers. This prior art design may be classified as a center feed design, whereby ink is fed to the vaporization chambers from a central location then distributed outward into the vaporization chambers. Some disadvantages of this type of prior art ink feed design are that manufacturing time is required to make the hole in the substrate, and the required substrate area is increased by at least the area of the hole. Further, once the hole is formed, the substrate is relatively fragile, making handling more difficult. Further, the manifold inherently provides some restriction on ink flow to the vaporization chambers such that the energization of heater elements within the vaporization chambers may affect the flow of ink into nearby vaporization chambers, thus producing crosstalk. Such crosstalk affects the amount of ink emitted by an orifice upon energization of an associated heater element.